Runoff and soil erosion from disturbed soil such as steep slope areas can be especially severe due to the potential for highly erosive rainfall and runoff and the lack of well-established plants.
Efforts are usually made to create permanent vegetative cover as quickly as possible; however, large rainfall events during critical periods of vegetation establishment can often cause extensive soil loss.
Conventional processes for providing erosion control usually involve spraying a hydro-seeding mixture. This mixture usually contains the following components: seeds (mainly grass seeds but also other native plants: flowers, brushes, trees), synthetic and/or natural soil conditioners (polyacrylamide polymers also called PAM, seaweed or plant extracts), soil amendments (such as mineral based on gypsum, lime, calcium carbonate, or organic based on crop residues or animal dejections), fertilizers (liquid or solid, organic or mineral), mulches (such as natural fibres based on straw, wood, cotton, or coco, or synthetic fibres based on paper or plastic). These components are then mixed and/or dissolved in water and finally sprayed over the area to stabilize.
Such mixtures have been shown in previous studies to improve infiltration, decrease runoff, and decrease soil loss. These studies are related in different articles written by Wallace & Wallace in the “Soil Science” Magazine such as “Control of soil erosion by polymeric soil conditioners” Volume 141, Number 5, page 363, dated May 1986. Moreover, a study report (WI 06-98) published by the Department of Transportation of Wisconsin (USA) in January 2001 clearly shows that polyacrylamide significantly reduced soil erosion and improved seed germination when used in hydroseeding compositions. For example, a test project called “CTH N” was implemented in October 1997. Data on the eroded soil of the test plot (polyacrylamide+seed) showed it was seven times smaller than the control plot (Seed only). Similar results were observed on seed germination. The seed germination rate of the test plot (polyacrylamide+seed+mulch) was 84%. This was 37% higher than that of control plot (seed+mulch).
PAM is a synthetic, high molecular weight organic water-soluble (meth)acrylamide (co)polymer. PAM can be manufactured as a neutral, cationic, anionic, or amphoteric and with varying molecular weights.
PAMs are used extensively worldwide for water and wastewater treatment, manufacturing paper, mining and drilling applications, and many other industrial applications.
The effectiveness of using a negatively charged (anionic) PAM as soil stabilizer is reported in many erosion control projects for many years (such as irrigated agriculture, construction sites, hydroseeding for slopes and highway shoulders). The present PAMs used in this industry are sodium-based polymers (see for example U.S. Pat. No. 6,562,882 which discloses the same composition as WI 06-98).
The performance of anionic PAM in controlling erosion is based on the fact it forms ionic bonds of smaller soil particles together to form larger particles. This makes the soil more resistant to the erosion forces of dispersion and shear. Further, the PAM enhances the intrusion of water into the soil, resulting in increased soil moisture to promote seed germination, lower runoff, and less soil detachment from erosion. Comparison of the PAM with other erosion control products that are currently used shows that this product is effective in controlling erosion. In addition, it is relatively inexpensive when compared to erosion mat, very easily applied, is not affected by weather conditions, and when applied following the manufacturer's recommendations is environmentally safe.
The improved process of the present invention, in one of its aspects, is to use potassium and/or ammonium based PAM (NH4/K PAM) instead of sodium-based PAM into the aforesaid hydro-seeding mixture so as to enhance the results of the process.
Specifically, the PAM of the invention may be mixed into the hydro-seeding mixture (comprising at least water and seeds) and the resulting mixture is sprayed over the soil in a water spray.